Apparatus for the manufacture of yeast



June 9, 1936. E. VAN THIEL. 2,043,940

APPARATUS FOR THE MANUFACTURE OF YEAST Filed Jan. 19, 1954 g my@ E ll//lL 11111 n I l will l gmc/VMM U, fffwy MMM/:45.5

Patented Jun-e 9, 1936 UNITED STATES APPARATUS FOR THE MANUFACTURE 0FYEAST f Emile van Thiel, Compiegne,-France, assigner to NaamloozeVennottschap Industrieele Maatschappij Voorhee Deventer, Nethe erlandsNou'ry and van der Lande, ands, a company ofthe Neth- ApplicationJanuaryl 19, 1934, Serial No. 707,387

In the Netherlands January 11,1933,

' 1 claim. (ci. 195.-142) The presentinvention relates to apparatus forpreparing yeast. More particularly )the present inventionrelates tomethods of preparing aerated yeast, i. e., a method-of aerating the mashduring the growth of the yeast.

The manufacture of aerated yeast which began several decades ago,constituted a definite advance in the art.` However, the earlier methodsof aerating the growing yeast involved certain technical diiiculties,some oi which had not been satisfactorily solved prior to the presentinvention as will more fully appear hereinafter.

In order to satisfy the oxygen requirements of growing yeast cells,ithas becomethe practice to introduce air into "the, fermenting liquidcontaining the growing yeast. In carrying this procedure into effect, itis common practice to first compress air and then conduct it into theyeast producing medium where it is liberated through' very smallorifices 'disposed in a set of air conductingy tubes 'or thelike,'located at the bottom of a, container in which the yeastproduction, is taking place. The order of magnitude of the.

diameters of the'said orifices is in some cases approximately 0.2 mm.and'when of this size they usually number about v50,000persquare meter`of nozzle tubes or the like. vThis would amount to about 25,000 of suchoricesper square meter of tank bottom. However, aftr escapeof thebubbles of compressed air from the orifices, the volume of the bubblesincreases up to about 20 cubic mm. The energyrequirements for^compressing the air to the extent required, amount to about 700 horse powerhours per 1,000 kilograms l45 cohol produced in the yeast medium lsvolatilized and remoyed therefrom with the v,escaping air,

.l and lost. The greatest part of the air didhoweverfunction to'eliminate carbon dioxide from the yeast producing medium and tomaintainthe latter in astate of' agitation, 'thus continuously bringing freshnutrient 'matter into contact with' the growing Yeast.- v

For the above reasons, it has, been generally recognized in the art thatit is necessary, to increase the'emciency of the process, to provide'fthe invention.

bubblesof very dimensions in the liquid lmedium, in order that a largesurface of the bubbles be available for contact with the liquid mediumvcontaining the yeast 'and at the same time to reduce the rate of flow ofthe air bubbles 5 through the liquid medium, but prior to applilcantsinvention, no one had devised means for accomplishing this result.

It has been found 'by other investigators that reducing the diameters ofthe orifices through 10 which the compressed air-escapes in the .liquidmedium, containing the growing yeast, to about 100 to 0. 16 microns,resulted in economy in air. Bubbles of air escaping from these orificesre-f. suited` in the eeonomizatlon of over of the 15 air, but the powerconsumption had to lbe increased to compensate for theincr'easedfrietlonal resistance resulting from thepassage of -air through theminute orifices. Other technical difficulties arose in this process,such asl clogging 20 and infection of the orifices, breakage and otherdifficulties in sterilizing. For these reasons andJ others, the methodhas proved impractical.

It has new been found that an'extremely line division of the air bubblesin the liquid medium 25 containing the yeast may be effected byconducting the a'ir-in large bubbles in the liquid medium Vandthereafter subdividing these bubbles in the same medium by forcing themthrough an aerating device whichalso acts as a; stirring device. 30 Ithas been` further found that this process results in good agitation ofthe liquid medium and also results in a much lower power consumption. Ithas been found that the present method of introducing the air andstirring resume in the' 35 production of ayeast of excellent 'qualityand in excellent yields. The power consumption is approximately 200horse power hours per 1,000 kilograms of yeast produced and theextremely, fine.

state of the air bubbles necessitates only about 4.0l

5% to 10% of the quantity of' air previously used.

The present `invention has resulted fronran entirely new line of attackof the. problem, as

compared with prior investigations, because instead of introducing theair intothe liquid medi- 45 um containing the yeast in the form ofextremely small bubbles, the `present process is such that large bubblesare introduced vand thereafter forced through a 'stirring device forexample a centrifugal stirrer. '111e rapid rotation ofthe 50stirringelement causes the air bubbles to be flnely divided, as will bemore. fully explained presently. i

Referringy to the' accompanying drawing the -l Figure 1 illustrates apreferred modification of Figure 2 is an enlarged view of the aircomminuting structure of Figure 1.

A represents a fermenting tank in which is positioned a rotating shaftB, whose lower end is integral with the rotor E. The ring or downturnedflange of the rotor is provided with many (say 25) channels a, (seeFigure 2). Beneath the rotor is placed the stator D which rests uponsupports G, and air is supplied through lpipe C. The stator also isprovided with many (say 8) channels b, in its down-turned flange asshown in the drawing. The stator and the rotor are preferablyinverted-dish-shaped members and preferably are arranged so .that thestator is nested within the rotor with a slight clearance between thetwo members as shown in the drawing, that is to say the internaldiameter of the rotor is slightly larger than the external diameter ofthe stator andthe rotor is positioned slightly above the stator. Theair, introduced through the air pipe C bubbling through the liquidmedium containing yeast and yeast food, is caught by the stator. Therevolving shaft B with rotor E will suckliquid and air through thechannels a and b, thereby cutting the big air bubbles into very ne ones.

For a fermenting tank of 25 m3 contents, an air pipe with a diameter of1 inch is usually suillcient. The diameter of the rotor is approximately20 inches. and that of the channels a and b 1 inch. The shaftmay'revolve with 200 revolutions per minute.

A further advantage of the suction produced by the motion of the rotor,is that the pressure of the air does not need to be more than thatnecessary to compensate the hydrostatic presi sure of the liquid in thefermenting tank.

The advantages of the above described process are that the parts of thedevice coming in contact with the liquid nutrient medium are easilycleaned and sterilized, a large saving in power consumption is effected.an enormous sav- This described device and process of aerating liquidsmay be adapted to all known yeast manufacturing processes,l for example,to those processes where all-the yeast food is added at the beginning ofthe process, or to those processes 5 where parts of the yeast food areadded during the process. The temperatures to be maintained during theprocess in the vessel are normal ones known to those skilled in the art.

Only about 5 to Y10% of the air heretofore re- 10 quired is needed inthe present process to obtain the same yield of yeast.

Example- A fermenting vessel, as described, is lled about two-thirdsfull with a solution of yeast nutrient. Mother yeast is incorporated l5and at the same time the aeration is started. During the fermentationadditional amounts of liquid yeast nutrient are added in the knownmanner. The, temperature is maintained between 26-33. C. After the totalamount of yeast 20 nutrient is added the aeration is continued for aboutone hour, whereafter the yeast is separated, washed and pressed.'

I claim:

An apparatus for propagating yeast'in a nutri- 25 ent liquid mediumwhich comprises a receptacle for containing a,bulk of such liquid mediumcarrying yeast, and means for introducing air into said receptacle atbelow a nested inverted-dishshaped stator-rotor combination located inthe 30 lower portion of said receptacle. in which there is provided aninverted-dish-shaped stator having perforations in its down-turnediiange, and an inverted-dish-shaped rotor of a slightly larger diameterthan said stator and being located only slightly above said stator, theinverteddish-shaped rotor also having perforations in its down-turnedflange, the down-turned flange of the rotor surrounding and spaced onlyslightly away 4from the down-turned flange of said stator, 40 and meansfor rotating said rotor at high speed for producing centrifugalcomminution of the air into said liquid mixture, whereby a volume of aircan be very thoroughly incorporated into the said bulk o'f nutrientmedium, and whereby a 45 small volume of air can serve to aerate a largevolume of the liquid mixture with the expenditure of only a small amountof power.

